There are many types of protocols for transmitting data from one or more servers to one or more hosts. For example, according to unicast-type protocols, a server sends a data transmission to a single-host. The server encodes each packet of the transmission with an indication of the host for which it is intended (e.g., a Media Access Control (MAC) address, an IP address, etc.). Packets are then transmitted from the server to the host, often via one or more intermediate routers. The unicast-type transmission protocols work well for data transmissions between a single server and a single host.
Multicast-type transmission protocols are often used when there is a need for a server to send duplicative data to multiple hosts. Examples of such situations may include streaming video or voice, news streams, multi-point conferencing, etc. According to many multicast-type protocols, a server transmits each packet a limited number of times (e.g., once). Instead of being directed to a single host, a multicast transmission may be directed to a multicast group address. Hosts may subscribe to the multicast group address at one or more routers. Routers servicing one or more subscribing hosts may also subscribe to the multicast group address, for example, at an intermediate router. To effect a multicast transmission, the server may generate data packets indicating the multicast group address as the recipient. Each data packet may be initially sent to a first router. The first router may create a duplicate of the packet for each host and/or router that is subscribed to the multicast group address at the first router. Subsequent routers may operate in a similar manner until all subscribing hosts receive the packet.
In order to test communications software and/or hardware, developers often emulate different data transmission protocols. One aspect of emulation involves modeling channel impairment conditions that may exist in live networks. For example, data packets transmitted over a network may be impaired due to limitations or errors in hardware, software, transmission media, etc. Because different hosts may be at different positions on a network, each host may have different channel impairment conditions. Existing network channel emulators, however, operate either prior to host devices or at the network level of host devices. This only allows them to apply channel impairment parameters based on recipient addresses.